Soil humus, consisting of organic residues from the decomposition of plant matter, is known as an important soil constituent for enhancing the growth of plants. The formation of soil humus depends upon an adequate supply of raw organic residues and upon suitable conditions for their decomposition. Should either condition be lacking, the eventual decrease in soil humus content leads to reduced soil fertility. In these cases, the addition of organic matter is necessary to increase the fertility of the soil.
Humic acid, defined as the portion of soil humus that is soluble in alkaline solution, but insoluble in acid solution, is the form of organic matter that often is added to the soil to increase fertility. Humic acid is found in rotting vegetable matter and can be detected in the black slime of an ordinary compost pit in a home garden. It also is found in the brown organic matter of a variety of soils, as well as in peats, manure, lignite, leonardite and brown coals. Humic acid does not have a single unique structure, but is a mixture of intermediate chemical products resulting from the decomposition and conversion of lignin and other plant materials to hard coal. Humic acid apparently is formed by the bacterial and chemical degradation of plant tissue, but in soils it also can be formed by certain secondary processes such as polymerization of polyphenols leached by rain from surface leaf litter, and condensation of phenols, quinones, and proteins that are provided by the action of soil micro-organisms and small animals on soil carbohydrates. As a result, humic acid is best characterized in terms of its origin and soil environment, rather than in rigid terms of chemical composition or chemical properties.
Humic acid has been used either as a soil amendment or as a fertilizer component to increase the fertility of soils. For instance, in U.S. Pat. Nos. 3,111,404, 3,264,084 and 3,544,295, Karcher discloses a complex and expensive method of producing a dry ammonium humate fertilizer by treating a humic acid-bearing ore, such as leonardite, first with phosphoric acid, then with ammonia, in order to extract the humic acid content. Burdick, in U.S. Pat. No. 2,992,093, teaches a similar extraction process yielding dry humates useful as soil conditioners and fertilizers. Particulate ammonium humate fertilizers are disclosed by Cooley in U.S. Pat. No. 3,418,100.
Another method of extracting humic acid from a humic acid-bearing ore is disclosed in U.S. Pat. No. 3,770,411 to Chambers, whereby a liquid humate product is obtained by reacting the ore with ammonia, then with phosphoric acid and, if desired, micronutrient elements. Schwartz et al in U.S. Pat. No 3,398,186 discloses using either an aqueous sulfate salt or a caustic soda solution as the extracting solution, followed by acidification to yield humic acid. In U.S. Pat. No. 3,076,291, Gardner teaches using ammonium, potassium, or sodium hydroxide to produce a humic acid-based seed germination promoter. Firth, in U.S. Pat. Nos. 4,274,860 and 4,321,076, discloses utilizing a humate derived from rutile sand deposits to stimulate growth in foliage plants. U.S. Pat. No. 4,319,041 to Goff discloses a method of forming a liquid humic acid product by mixing a humic acid-bearing ore, such as leonardite, with water and caustic soda.
The methods and compositions disclosed in the prior art are generally difficult and/or impractical to prepare and use. The disclosed methods are complex, involve large and expensive machinery, and usually produce granular materials. The prior art methods for producing the granular humates further suffer in that a substantial amount of the micronutrient elements essential to plant growth are extracted and removed during processing of the humic acid-bearing ore to a granular humic acid product. Methods of producing granular humates are also expensive, time-consuming, and require extra machinery to dry the humic acid product before packaging and use.
Therefore, it is highly desirable to provide a liquid humate product and thereby take advantage of easier storage, shipment, use and handling of a liquid product, of avoiding the extra step and cost of drying the product, and of direct application of the humate product by systems such as irrigation and spraying systems. However, the prior art methods of making liquid humates possess the serious disadvantages of low solids content and the presence of inactive and insoluble constituents. Consequently, several of the commercially available liquid humate products are only partially comprised of active humic acid solids, with the remainder of the advertised solids being inactive water-soluble constituents or inactive water-insoluble constituents that often plug irrigation and spray equipment.
Accordingly, it would be advantageous to provide a method of producing a highly concentrated aqueous solution of humates, such that insoluble constituents are minimized or eliminated and such that the solids content of the liquid is predominantly comprised of active humic acid salts as opposed to inactive soluble constituents. It also would be extremely advantageous to incorporate other additives, such as a plant nutrient component, into the liquid alkali metal humate product to dramatically increase the effects of the humate salt upon agricultural and horticultural crops. As a result, the amount of humate-containing product applied to the crop could be reduced in order to obtain the same crop yield, or the unreduced amount of humate-containing product could be applied to obtain superior crop yields.
Any method utilizing a liquid alkali metal humate in combination with additives to synergistically increase the effect of the humate would enhance and broaden the use of liquid humates in the agricultural and horticultural areas. Preferably any such method should utilize an economical, easy-to-manufacture liquid humate product possessing qualities that positively affect crop yield, such as number of fruit per plant and size per individual fruit.